[Old Otto]

alright guys here we go, all gauges work except the tachometer and clock. i pulled out the instrument cluster and checked to see if the connections were o.k. and they were, so where do i go from here? everyone once in a while the tachometer will work and sometimes it acts possessed and goes crazy, but then goes right back to sleep. so do i need to find another tachometer gauge? or is it something more dastardly?

ty,
gordon

 

[NordRhein]

A 300SD drives the tach with a black box called an amp instead of the ignition control module which is not present. I would suspect that the amp is fried or it's sensor.
The clock probably died like they all do - it needs new capacitors.

 

[JamesDean]

hey
try this:
http://electric.articles.*/300tachamp/
Mine was acting just like yours, it would come on for a little while and then die. Occassionally it would go all back and forth from left to right with no reason, I was at a stop sign. Hope that helps.

 

[JamesDean]

why wont they let me put the website in grr

well anyway ill just paste in the info...

Open your hood up, look on ur right side fender, just above your hub for the wheel. See that black cylinder (ususally its held down with 2 screws and has a plastic strap coming off it) ? That's your tach amplifier. It's the reason your tach stopped working.
It's really easy to fix though, you just unscrew it, then pull off the top (that can be kind of tough, just pull); once you have it off, remove the tach amp from inside the casing.

Now find yourself a piece of foam, cardboard or the filter from a cigarette, and stick it in the case. Put the tach amp back in with the pins facing out, then screw it back onto the car.

Your tach will work now.

This works because the pins are floating in a was of silicone cement, and over time they aren't being pushed properly into the sockets of the part that mate with. By sticking a bit of stuff in the cap you're forcing the pins to be a bit lower where that actually make contact.

If this doesn't fix your amp, or more likely, you've had to do this a few times, then you either need to get a new tach amp from Beckman Instruments, or if you're adventurous you could try rebuilding yours. The electrics work, but the pins aren't making contact. I've never done this, but I suspect chipping away a bunch of the silicone and squirting some epoxy in there to anchor the pins might work.

Late breaking news: some dialectric grease applied to the pins seems to work longer and better when used on conjunction with the above quick fix.

If this doesnt work you may need a new tach amp.

--Kris

 

[Old Otto]

so mcgyver-ish, i love it. ill give it a try tomorrow, thx a million for typing that all out. []

 

[Old Otto]

cigarette trick worked like a charm, i used a marlboro light 100 filter, it seems to be giving me better results then the pall mall menthols []

good thing one was on the ground in front of the house, i would hate to have spent the 7 bucks on a pack []

 

[JamesDean]

I just used a chuck of cardboard from some random box...seemed to do the trick.
Next task...RE-ENABLING THE CRUISE CONTROL! (my grandfather had it disabled, I dont know why)

 

[tmnoonan]

Worked like a charm!